(57) A surgical appliance for forming an opening through the skin of a patient takes
the form of a trocar (10) which can be expanded by inserting an expander (12) through
the proximal end and moving it towards the distal end.
In one aspect of the invention, the trocar is a tube partially divided by cut-away
openings in the tube, into two component portions which are preloaded into a closed
condition in which they converge towards the distal end, so that the expansion is
against the preloading. In a second aspect, the trocar has two or more components
and one or more cutting edges at the distal end which extend across substantially
the full width of the distal end and the arrangement provides that the cross-section
of the trocar does not increase towards the distal end in the open condition. Taken
together, the features of the second aspect minimise the danger of tearing the skin.
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